The present invention relates to powder dispensing mechanisms and more particularly to an automated apparatus for accurately and rapidly dispensing measured quantities of powder to containers in one or more arrays.
Although the present invention has been developed for use in pharmaceutical laboratories to automatically perform accurate and rapid weighing of milligram quantities of resin powder into trays carrying arrays of NanoKans, this apparatus is suitable for many other applications in which precise quantities of powder must be dispensed quickly and efficiently. Thus, while the invention will be described in the context of the pharmaceutical application for purposes of illustration, the invention should not be construed as being limited to that particular environment.
Many pharmaceutical applications require the introduction of relatively small quantities of powders which must be accurately measured by weight. In practice, this has proven extremely difficult to accomplish, particularly if precisely measured quantities of the powder must be dispensed rapidly into large numbers of containers.
The flow characteristics of powders vary widely due to particle size, electrostatic properties, the effects of variations in humidity, the surface properties of the particles and the tendency of the particles to adhere to various surfaces. Many different types of powder dispensers have been utilized, including those employing suction and vibratory type feed mechanisms, as well as single and double screw conveyors with various pitches and configurations. However, for one reason or another, none of these known powder dispensers has proved to be sufficiently accurate and rapid for use under all conditions.
Examples of screw type dispensers are found in U.S. Pat. No. 4,844,296 issued Jul. 4, 1989 to Torahiko et al., entitled xe2x80x9cApparatus and Method for Quantitatively Delivering Food Materialsxe2x80x9d, in U.S. Pat. No. 4,804,111 issued Feb. 14, 1989 to Ricciardi et al., entitled xe2x80x9cMechanism For Metering Solid Materials Which Flow in a Manner Similar to Liquidsxe2x80x9d; and in U.S. Pat. No. 5,421,513, issued Jun. 6, 1995 to Gubler, entitled xe2x80x9cConveying Device for Exact Metering, Wherein At Least One Projecting Body is Rotated in an Inner, Disrupted Threaded Groove, and a Use Thereforxe2x80x9d. The Gubler patent discloses an approach to the problem of surface adherence which utilizes brushes and a sleeve with inner threaded grooves.
The present invention also employs a screw-type conveyor but differs from the screw conveyors of the prior art where the screw is situated within a rigid enclosure with the edge of the screw blade spaced from the interior surface of the enclosure wall. In the present invention, a vertical screw is situated within a compliant sleeve with the screw blade in direct contact with the interior surface of the sleeve wall, resulting in a positive feed system in which the quantity of powder being dispensed can be very accurately controlled, under all conditions, even when the powder is dispensed rapidly.
This is accomplished by utilizing a section of conventional silicone tubing as the sleeve which surrounds the screw so as to form a confined helical channel within the sleeve along which the powder is moved as the screw is rotated. The inner diameter of the silicone tube is selected to be slightly smaller than the outer diameter of the screw blade such that the edge of the screw blade continuously bears against the interior tube wall causing the wall to deform slightly proximate the area of blade contact. However, the silicone tube surface is smooth and resilient enough not to interfere with the rotation of the screw.
This configuration provides a positive feed and at the same time prevents powder from flowing between the screw blade and sleeve wall, and thus out of the bottom of the tube, when the screw is not rotating, such that the quantity of powder dispensed from the bottom of the sleeve can be accurately controlled. The screw maintains a constant but gentle pressure on the powder when it is rotating, without harming the powder.
The screw dispenser is capable of rapidly depositing powder into a plurality of containers, such as NanoKans, in an array. The container array is situated in a tray which rests on a scale platform. In order to enhance the speed and accuracy of the dispensing process, the rate of screw rotation for each dispensing operation is relatively high during the initial time period, when the bulk of the powder is dispensed. After a given time interval, the rotation rate of the screw is decreased and powder is dispensed more slowly, until the required weight of powder has been dispensed. The scale need be operational only during the latter period because it is only important to monitor the weight of the dispensed powder carefully as it approaches the desired level in order to deactuate the motor which drives the screw at the precise time when the desired weight of powder has been dispensed.
Automation of the dispensing process is achieved by moving the powder dispenser assembly sequentially along positions in a X-Y plane, above the powder receiving containers, and then along the Z plane to insert the assembly into each container. The dispenser assembly is moved stepwise between the dispensing positions to align it with each container in the array by a computer controlled plotter-type mechanism. One way to accomplish this is to modify a conventional Gilson liquid handler by replacing the liquid dispensing probe with the powder dispenser assembly of the present invention. Computer control is employed to cause the powder dispenser assembly to move sequentially through the dispensing positions to align with and be inserted into each of the containers of the array, and for actuating the drive motor for the screw to dispense a measured quantity of powder to each container, in turn.
Preferably, a bifurcated bracket is employed to simultaneously position two separate powder dispenser assemblies. Each assembly fills the containers in one of two separate trays, each tray being independently weighed by separate scales. In this way, two different powders can be dispensed simultaneously or twice as many containers can be filled at a time with the same powder.
It is therefore a prime object of the present invention to provide automated apparatus for rapidly dispensing precisely measured quantities of powder to containers in an array.
It is another object of the present invention to provide a powder dispensing assembly in which a screw is rotatably received within a compliant sleeve with the screw blade in direct contact with the interior surface of the sleeve.
It is another object of the present invention to provide a powder dispensing assembly including a screw controlled to rotate within a compliant sleeve at a relatively high rate during an initial time period and at a slower rate thereafter.
It is another object of the present invention to provide computer controlled apparatus which sequentially moves a powder dispensing assembly to predetermined positions relative to containers in an array.
It is another object of the present invention to provide an automated apparatus for rapidly dispensing precisely measured quantities of the same or different powders into containers in separate container arrays.
In accordance with one aspect of the present invention, a powder dispensing assembly is provided. The assembly includes a powder reservoir with an outlet. A compliant sleeve having an inner surface is situated proximate the reservoir outlet. A rotatable screw with a blade is provided. The screw is received within the sleeve with the blade is in contact with the inner surface of the sleeve. Drive means for rotating the screw relative to the sleeve are provided.
The outer diameter of the screw blade is at least as large, and preferably slightly larger, than the inner diameter of the sleeve. This insures that direct contact is maintained between the screw blade and the sleeve.
The sleeve preferably takes the form of a section of a silicone tube.
The assembly further comprises a rigid tube. One end of the rigid tube is received within the sleeve, spaced a short distance from the end of the screw. The other end of the tube preferably extends beyond the sleeve.
The rigid tube has an outer diameter. The outer diameter of the screw blade is approximately equal to the outer diameter of the rigid tube.
The compliant sleeve has an inner diameter. The outer diameter of the rigid tube is approximately equal to the inner diameter of the compliant sleeve.
The reservoir outlet has an outer diameter. The complaint sleeve has an outer diameter. The outer diameter of the reservoir outlet is approximately equal to the outer diameter of the compliant sleeve.
The reservoir outlet has an inner diameter. The inner diameter of the reservoir outlet is larger than the outer diameter of the screw blade and the inner diameter of the compliant sleeve.
Means are provided for retaining the compliant sleeve proximate the reservoir outlet. The retaining means comprises a second compliant sleeve, preferably in the form of a section of silicone tube. The retaining means surrounds the reservoir outlet and the sleeve.
The reservoir outlet has an end. The retaining means retains the compliant sleeve adjacent the end of the reservoir outlet.
Means are provided to removably connect the drive means and the screw. The connecting means partially extends through the reservoir. The screw is affixed to the connecting means and extends through the reservoir outlet. Means are provided for mounting the screw drive means above the reservoir.
The connecting means comprises a first part moveably mounted on the motor output shaft and spring loaded to engage a second part to which the screw is connected. The first part has a recess into which the second part is received. The recess and second part are correspondingly shaped to form a drive link when engaged. The second part is disengaged from the part to permit removal of the reservoir by moving it away from the first part, against the spring.
The reservoir has a main section and an inlet section. The inlet section extends from the main section. Preferably, the inlet section extends outwardly and upwardly from the main section.
Means are provided for controlling the drive means to rotate the screw at a first rate during a first time period and at a second rate during a second time period, for each dispensing operation. The first rate is higher than the second rate.
The assembly is adapted to dispense a predetermined weight of powder into a container. Means for weighing the container and for generating signal that is a function of the weight of powder in the container are provided. The control means receives the weight signal and deactuates the screw drive means when the predetermined weight is reached. The weighing means is operational only during the second, decreased rotation rate time period.
The assembly is adapted to dispense powder into a plurality of containers in an array. Means are provided for moving the assembly into alignment with each of the containers in the array, in sequence.
The assembly moving means includes a bracket to which the assembly is mounted. Means are provided for moving the bracket to selected positions relative to the array. The positions are selected such that the assembly aligns with a different one of the containers in each of the positions. The moving means moves the bracket along positions relative to the containers in the array.
Means are provided for weighing the array. The weighing means includes a surface upon which the array is situated and means for aligning the array with the bracket moving means.
The array is preferably situated in a tray. The aligning means includes a track fixed relative to the bracket moving means and a part having a surface adapted to abut the tray. The part is movable along the track. The track and the surface are in a fixed relationship, preferably orthogonal, to each other.
Powder may be dispensed into a plurality of containers situated in first and second arrays. To accomplish this, first and second powder dispensing assemblies are provided. Means are provided for simultaneously moving the first and second powder dispensing assemblies into alignment with the containers in each of the first and second arrays, respectively.
The assemblies moving means includes a bifurcated bracket. The bracket has first and second branches to which the first and second powder dispensing assemblies are respectively mounted. Means are provided for moving the bracket to selected positions relative to the arrays. The positions are selected such that each assembly is aligned with a different one of the containers in each of the arrays, in each of the positions. The moving means preferably moves the bracket to positions in the plane.
Means are provided for weighing each array. The weighing means includes first and second platforms upon which the first and second arrays are respectively received.
Means are provided for aligning each of the arrays with the bracket moving means. Each of the arrays is situated in a tray. The aligning means includes a track, situated between the scale platforms. The track is fixed relative to the bracket moving means. A part having first and second surfaces is adapted to abut the first and second trays, respectively. The part is moveable along the track to align the arrays. The surfaces are collinear. The collinear surfaces are fixed relative to the track.
In accordance with another aspect of the invention, automated apparatus for dispensing measured amounts of powder to containers in an array is provided. The apparatus includes an array of containers and a powder dispensing assembly. The assembly includes a powder reservoir with an outlet. A compliant sleeve is situated proximate the powder reservoir outlet. A screw is at least partially received within the sleeve. The screw has a blade which is in contact with the inner surface of the sleeve. Drive means are provided for rotating the screw. The assembly is mounted on a bracket. Means are provided for moving the bracket relative to the array to selected positions in which the assembly aligns with the containers in the array. Means for weighing the array and for generating a signal in accordance with the sensed weight are provided. Means for controlling the screw drive means in accordance with the signal are also provided.
The drive means is controlled to rotate the screw at a first rate during a first time period and at a second rate during a second time period, for each powder dispensing operation. The first rate is higher than the second rate. Means are provided for actuating the weighing means at the beginning of the second time period for each dispensing operation.
Means are provided for aligning the array with the bracket moving means. The array is situated in a tray. The aligning means positions the tray relative to the bracket moving means. The aligning means includes a track mounted in fixed relation to the bracket moving means and a part with a surface adapted to abut the tray. The part is movable along the track. The surface is in a fixed relation, preferably orthogonal, with the track.
In accordance with another aspect of the present invention, automated apparatus for dispensing measured amounts of powder to containers in first and second arrays is provided. The apparatus includes first and second powder dispensing assemblies. Each of the assemblies includes a powder reservoir with an outlet. A compliant sleeve is situated proximate the reservoir outlet. A screw is at least partially rotatably received within the sleeve. The screw has a blade which is in contact with the inner surface of the sleeve. First and second drive means for rotating the screws in the powder dispensing assemblies, respectively, are provided. Each of the assemblies is mounted on a bracket. Means are provided for moving the bracket relative to the arrays to selected positions in which each of the assemblies aligns with the containers in a different one of the arrays. Means for weighing each of the arrays and for generating first and second signals in accordance with the sensed weight of the first and second arrays, respectively, are provided. Means for controlling the first and second drive means in accordance with the first and second signals, respectively, are also provided.